The present invention relates to an apparatus for and a method of manufacturing information storage mediums such as video discs or digital audio discs in which vast amounts of information are recorded per unit area of the disc.
It is customary practice to fabricate phonograph records or discs by feeding a pair of spaced record labels into an extruding machine, extruding a mass of synthetic resin between the record labels into a pancake or biscuit, and then transferring the pancake to a press in which it is pressed into a disc with sound grooves cut thereon.
Video discs containing both video and audio information are in the form of a flat circular plate, typically about 26 cm across, made of vinyl chloride which is rendered electrically conductive by being mixed with 5% to 30% by weight of carbon. The video disc has on each of its surfaces a spiral track containing a series of depressions or pits written by frequency-modulated signals, with adjacent track convolutions or turns being closely spaced as at a pitch of 1.35 .mu.m. The information can be read out of the spiral track by picking up variations in electrostatic capacity produced between the pits and a diamond needle having a metal film electrode which traces the spiral track as the disc rotates at a high speed of 900 revolutions per minute.
The video discs differ widely from the phonograph records in that the video discs contain a great amount of video and audio information recorded at an extremely high density. Many uses and applications which have been, and will be, found by the video discs especially for the development of educational and cultural aspects of life would certainly benefit from mass production of video discs of high quality.